Fixes #9720
Fixes #8053
Fixes https://code.google.com/p/thread-sanitizer/issues/detail?id=89

Change-Id: I7d598e53de86586bb9702d8e9276a4d6aece2dfc
Reviewed-on: https://go-review.googlesource.com/4950Reviewed-by: Ian Lance Taylor <iant@golang.org>